In Determining the Distance to a Galaxy by Using Observations

Multiple Choice

In determining the distance to a galaxy by using observations of a Cepheid variable star, which of these properties is NOT needed?

A) average brightness or apparent magnitude of the Cepheid
B) velocity of the Cepheid via the Doppler effect
C) type of spectrum of the Cepheid-whether it is metal-rich or metal-poor
D) period of variability of the Cepheid